The present invention relates to variable valve operating apparatus suitable for improving engine starting performance.
There is a demand for accurate control of a valve timing (opening timing and/or closing timing) of an engine valve, especially of an intake valve at an initial stage of an engine starting operation, for recent stringent regulations against exhaust emission, and increase of frequency of engine restarts in a hybrid vehicle.
To this end, there are proposed various valve actuating apparatus for controlling the opening and closing timings of an engine valve in accordance with an engine operating condition by varying a relative rotational phase between a timing sprocket and a vane fixed to a camshaft by the use of oil pressure.
In the case of such a hydraulic actuating mechanism, when the engine speed is very low as in an engine starting operation, a control oil pressure is low and the hydraulic power for changeover is insufficient. Moreover, the actuating mechanism tends to receive an urging force in the direction to the retard side, opposite to the cranking rotational direction, and to suffer friction in various parts. Consequently, the changeover response speed to the advance side is liable to be low.
A published Japanese patent application publication number 2005-233049 shows a variable valve actuating system including a phase varying mechanism which is provided on an intake valve's side, and arranged to fix a vane at a relatively advanced position with a lock pin at the time of stop of the engine, and to enable a restart of the engine from the relatively advance position. The thus-constructed variable valve actuating system is expected to stabilize the combustion by providing an adequate valve overlap between the exhaust and intake valves, and setting the intake valve closing time closer to the bottom dead center improve the engine starting performance, and thereby to reduce cold engine emission and improve the engine starting performance.